It is recognized that fuel efficiency in a vehicle transmission can be improved by the provision of a lock-up clutch operable to directly connect the input of a hydrodynamic torque converter to the output thereof. In the past the typical lock-up clutch included a piston or clutch lock-up plate interposed between the forward wall of the converter. The forward wall is part of a rotatable housing driven by the output shaft of the engine and constitutes the input of the torque converter. The piston plate in turn is operatively connected to the transmission input shaft through the turbine hub of the converter which constitutes a clutch output member. In the past a vibration damper has been inserted between the piston plate and the turbine hub to dampen any torsional vibration occurring from the vehicle engine or other driving source such as the vehicle wheels when the vehicle acts to drive the engine when the torque converter or hydrodynamic converter and the transmission are in a coast mode.
Prior vibration dampers have included a clutch driven plate and a spring retainer plate secured together in spaced relation to receive a plurality of damper springs in windows formed between the spring retainer plate and a hub flange. As shown in U.S. Pat. No. 4,188,805, the damper assembly includes a hub with at least two radial arms, drive input means connected to the piston plate and axially aligned with the hub arms are floating equalizers journaled on the hub and having oppositely disposed arms, and damper springs positioned between the hub arms and equalizer arms; the drive input means being located in the path of the damper springs. Other mechanical spring dampers are shown in U.S. Pat. Nos. 4,139,995; 4,188,805; 4188,806; 4,232,534; 4,279,132; 4,302,951; 4,304,107; 4,333,552; 4,347,717; 4,360,352; 4,413,711; 4,427,400; 4,430,064; 4,451,244 and Re. 32,705; 4,530,673; 4,555,009; 4,585,427; 4,679,678; and 4,702,721 all owned by the assignee of the present invention.
While suitable for their intended purpose each of the dampers shown in the aforesaid patents require elaborate fixturing for assembly and involve use of a large number of spring components to provide a wide range of damping characteristics over various travel distances required for a particular coupling arrangement.
The present invention provides a simplified vibration damper assembly which relies upon hydraulic flow restriction to produce damping forces for controlling vibrations between the input member and output member of a hydrodynamic converter, e.g., the rotary housing of a converter which connects to the output shaft of a drive engine and an output hub of the converter which is adapted to be connected to the input shaft of a transmission for driving the output wheels of a vehicle.